The present invention relates to a method of forming or molding a circuitry by molding a resin on a plurality of bus bars inserted at a small pitch (at small intervals) in a mold, and the present invention also relates to a mold structure used in this molding method.
A circuitry, having bus bars, is used in an internal circuit of an electric part such as a connector. This circuitry is produced by inserting a plurality of bus bars into a mold and then by injecting a resin into the mold to form a resin-molded portion. As a result, the resin-molded portion holds the bus bars in such a manner that the adjacent bus bars are kept out of contact with each other.
FIGS. 4 and 5 show a related method of molding such a circuitry. A mold 1 has a cavity portion 3 in which a plurality of bus bars 2 are held in a juxtaposed manner. Holder pins 4 are provided in the cavity portion 3, and these holder pins 4 hold the plurality of bus bars 2 at small intervals in such a manner that the bus bars will not contact with one another. The holder pins 4 are arranged substantially on a common straight line in a direction of juxtaposition of the bus bars 2.
In this method, the bus bars 2 are juxtaposed in the cavity portion 3 of the mold 1 in such a manner that each bus bar 2 is inserted between the associated holder pins 4, and then the mold is clamped, and then molten resin is injected into the cavity 1 through a gate (not shown). The molten resin thus injected flows in between the bus bars 2, and is solidified to form resin-molded portions 5, and each resin-molded portion 5, formed between the associated adjacent bus bars 2, holds these bus bars 2 out of contact with each other, as shown in FIG. 5.
In the above molding method, however, the holder pins 4 and the bus bars 2 are arranged so densely that the resin can not easily flow in between the bus bars 2, and therefore the resin-molded portions 5 are liable to be formed with insufficient length (short shot). And besides, since the holder pins 4 are arranged such that each of the bus bars 2 is held at two juxtaposed points on a common line perpendicular to an extending direction of the bus bars 2, each holder pin 4 functions as a rotational fulcrum for the associated bus bar 2, so that the bus bars 2 are liable to be turned as indicated by arrows in FIG. 6. This results in a problem that the adjacent bus bars 2 are brought into contact with each other. Furthermore, since the holder pins 4 are arranged on a common line, the holder pins 4 are disposed close to one another as shown in FIG. 7. Therefore, the whole of each holder pin 4, including its base portion 4a, can not be made thick, and therefore the holder pin 4 has a reduced strength, and is liable to be broken.
It is therefore an object of the present invention to provide a method of molding a circuitry in which a short shot of a molded resin is prevented, and bus bars are prevented from being turned, and holder pins have an increased strength. Another object of the present invention is to provide a mold structure suitably used in this molding method.
In order to achieve the above objects, there is provided a mold structure for molding a circuitry comprising: a cavity to which a plurality of bus bars are juxtaposedly inserted provided with gap portions to which a resin material to be injected therethrough; and a plurality of holder pins provided on the respective gap portions and arranged alternatively in the juxtaposition direction of the plural bus bars to hold the respective bus bar to be inserted therebetween.
In the mold structure, each of the bus bars is held by both sides of the holder pins at two different points in an extending direction thereof.
In the mold structure, each of the holder pins has a large-diameter base portion, and the holder pins are arranged such that the base portions of any adjacent holder pins are overlapped in an extending direction of the bus bars.
Since the holder pins are arranged alternatively, the adjacent holder pins are sufficiently spaced from each other. Therefore, the holder pins and the bus bars are not arranged densely, and the resin can easily flow in between the bus bars, so that the short shot of the resin is prevented. And besides, the adjacent holder pins are contacted respectively with right and left sides of the bus bar at two different points in the extending direction thereof to thereby hold the bus bar, and therefore the bus bar will not be turned, and the bus bars will not be brought into contact with each other. Furthermore, the adjacent holder pins are sufficiently spaced from each other, and therefore the holder pins can be made thick to have an increased strength.
According to the present invention, there is also adopted a method of molding a circuitry, in which a plurality of bus bars are juxtaposed with predetermined intervals, comprising the steps of: preparing a mold structure comprising a cavity, and a plurality of holder pins provided with the predetermined intervals and arranged alternatively in the juxtaposition direction thereof; inserting the plural bus bars juxtaposedly into the cavity through respective spaces between the holder pins; injecting a resin material into respective spaces between the bus bars through the cavity; and solidifying the resin material to keep the bus bars out of contact with each other.